I wanted a river on my layout so I used a hot knife to get a rough cut in my foam base. I then planned to build it back up a bit to get the riverbed profile where I wanted it. I wanted the river bed smooth when finished so I decided to use some self leveling caulk I had on hand for my RV roof. Big mistake. The caulk attacked the foam and melted completely through 3" of foam. My bad for not testing it first.
Now I need to backfill the grand canyon I created. What would be a prefered product to build it back up. I have some Plaster of Paris as well as some Sculptamold on hand but I have no real experience with either of them. My goal is to build the foam back up to the profile I want for the river bed then later add the river water to finish it off.
Paul D
N scale Washita and Santa Fe RailroadSouthern Oklahoma circa late 70's
Can you use a regualr knife or hotknife to square up the area then filling it with solid foam cut to size? If too weak for that. maybe consider cutting the affected area out and placing the new foam in from below. Here is where some some bamboo skewers could help reinforce whatever glue works (without melting stuff, of course.)
Sculptamold might work if you can get it to fill the area when wet without breaking through. If that might happen, you could try several thin layers and et dry between layers as each will strengthen the area. Sculptamold will need some reinforcement (alumninum screening, etc) if it's expected to add structural reinforcement
Mike Lehman
Urbana, IL
Great Stuff Spray Foam. This will stick to your current foam. Assuming you have a hole in the foam where you can see the floor, cover the hole from the bottom with a piece of cardboard.
Spray foam expands tremendously. If you've alreadly laid track you need to take precautions so that it doesn't get ruined by the expanding foam. You will probably have to recontour the area after the repair.
If you have never worked with spray foam, what this video
I don't know how it cuts with a hot knife. Ron is a member of this forum. Not sure of his screen name.
Henry
COB Potomac & Northern
Shenandoah Valley
What about covering the hole with a smooth surface like a sheet of styrene, and then building back up the river banks with your plaster and Sculptamold? Depending on how deep you wanted the river.... it could work.
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So, you need to fill in 3" ? I would do what Mike L. suggested, caulk any joints between the pieces, and finish it off with the Sculptamold, or plaster. I probably would use dry wall mud, mixed somewhat stiff.
Anything you want to pour into the area, I would do in layers. 3" is a lot. Just make sure everything is sealed so whatever you pour into the crevice, won't leak out.
Mike.
My You Tube
PEDI decided to use some self leveling caulk I had on hand for my RV roof. Big mistake.
Ooops! I hope it wasn't too much of a mess to clean up.
Henry (BigDaddy) beat me to what I was going to suggest. The Great Stuff foam will adhere itself to the remaining foam extremely well and, like Henry's video shows, it will be easy to sculpt into the profile you want.
I have been researching various methods of building scenery bases for our new club layout and the expandible foam seems to be winning, not that it would be the only method that we will use.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
You don't say just how big of a oops . I picture a trench, daylight on the bottom.
If you could glue/caulk a pecie of foam across the bottom,and then just build your banks.I use plain ole latex caulk to glue foam. As said above skews work well for added support. I also use drywall mud,but the premixed. No mixing mess and less waste.
I don't care for great stuff, you have very little control , and you end up cutting and wasteing a lot. And altough possible,I never had luck trying to reuse a opened can.
As faras the plaster; mix as to directions,smear it on. Pretty hard to screw it up
Thanks all. Some great ideas. I did not think of using Great Foam but I think it will be perfect for my needs. I have used Great Stuff many time around the house so I know how it works. In the video, he used the high expansion foam but they also make a low expansion foam which I think will be best for my situation. Easier to control the expansion. If I use the low expansion foam to fill most of the hole then top it off with Sculptamold to get my final profile would work well.
Reguarding comments about "all the way through" - my blue foam has a thin film of something on both sides. The caulk melted thru all the foam but did not melt through the thin film. As a result, no mess under my layout and the thin film creates a bottom layer that will help me fill the hole
If you're experienced with using expanding foam, that can work (make sure it doesn't eat YOUR foam, first, though.) I'd still want to embed some reinforcement in it, so the skewers, aluminum screen, etc may still be a good idea to work into the foam before it sets.
My recourse would be to create a plate base under the foam, even if just some plywood or cardboard for convenience. Then I'd fill the 'canyon' with some popcorn foam package fill, tape over that, and then create a carved river bed using either drywall mud, Durabond, Durham's water putty, or exterior spackle. Exterior spackle would be my first restort because I always have some on hand and it is tough stuff. In fact, you'd want 90% of the shaping to be done when you first lay it because it's a bear to sand.
I used the low expansion foam and filled the hole. Worked except that it expanded more than I expected and had to carve some back out. I am now happy with the rough profile. I think I will apply ground goop to bring it to the final profile and then I can pour the liquid water.
There is a "gun" from great stuff that makes the can re-usable. I have had a can going for several weeks at a time, plus you get great control of how much and where you an place it.